Diphenyl ether and benzophenone compositions

ABSTRACT

A functional fluid composition comprises a homogeneous mixture of diphenyl ether and benzophenone and at least one additional component selected from the group consisting of dibenzofuran and naphthalene. In a more specific embodiment, a functional fluid composition comprises a homogeneous mixture of diphenyl ether employed in an amount from about 5 to about 80 weight percent, benzophenone employed in an amount from about 5 to about 50 weight percent, and at least one additional component selected from the group consisting of dibenzofuran and naphthalene employed in an amount from about 5 to about 25 weight percent, the diphenyl ether, the benzophenone, and the at least one additional functional fluid composition is thermally stable up to at least about 650° F. and has a freezing point of less than about 54° F.

TECHNICAL FIELD

This invention relates generally to functional fluids, such asheat-transfer fluids, lubricants, hydraulic fluids, and the like. Morespecifically this invention relates to functional fluids which containdiphenyl ether, benzophenone, and at least one additional componentselected from dibenzofuran and naphthalene.

BACKGROUND OF THE INVENTION

A currently popular heat-transfer fluid consists of a eutectic mixtureof diphenyl ether and biphenyl. The diphenyl ether/biphenyl eutecticmixture has good thermal stability up to 750° F. and, therefore, has amaximum recommended use temperature of 750° F. Unfortunately, the fluidfreezes at about 54° F. This high freezing point requires users toheat-trace their systems in order to start up or shut down anywhere thetemperature may drop below the 54° F. The need to heat-trace results inincreased capital, maintenance, and operating expenses. There existsother heat-transfer fluids which have lower freezing points (alsoreferred to as "minimum use temperatures") but they do not have highmaximum recommended use temperatures. Therefore, there is a need for animproved heat-transfer fluid having a low freezing point and arelatively high maximum recommended use temperature.

Additionally, there exist needs for improved lubricants and hydraulicfluids. The demands placed on these materials continue to undergosignificant changes. Lubricants and hydraulic fluids for futureautomotive and aeronautic applications will have requirements differentfrom those currently in use. For example, it is anticipated that engineswill operate at temperatures exceeding 480° F. and will be constructedusing materials different from those currently in use. Thus, what areneeded are new compositions useful as lubricants or hydraulic fluidsthat are stable at the high use temperature while possessing the otherproperties required of these materials.

Materials such as heat-transfer fluids, lubricants, and hydraulic fluidsmay be considered "functional fluids" because of their usefulness inmechanical operations. Examples of previous attempts of preparing suchfunctional fluids are described in the following patents.

U.S. Pat. No. 4,622,160 issued to Buske et al. on Nov. 11, 1986,discloses heat transfer fluids which are made by mixing methyl and/orethyl biphenyls with diethylbenzenes. The heat transfer fluids maycontain one or more extenders, which extenders include diphenyl oxideand/or biphenyl.

U.S. Pat. No. 4,054,533 issued to Watson on Oct. 18, 1977, disclosesheat transfer fluids consisting essentially of about, by weight: (a) 20to about 40 percent of diphenyl ether, (b) 40 to about 60 percent of a2-biphenylyl phenyl ether and 4-biphenylyl phenyl ether mixture, and (c)12 to about 25 percent of a polyphenylphenol mixture. Minor amounts,typically less than about 7 weight percent, of various impurities may bepresent, which impurities include phenylnaphthalene,methylphenylnaphthalene and the like. U.S. Pat. No. 3,966,626 issued toJackson et al. on Jun. 29, 1976, discloses heat transfer agentscontaining at least about 20 volume percent diphenyl oxide and at least20 volume percent biphenylyl phenyl ether, polyphenyl ether or mixturesthereof.

U.S. Pat. No.3,931,028 issued to Jackson et al. on Jan. 6, 1976,discloses that a well-known heat transfer fluid consisting essentiallyof the eutectic mixture of diphenyl oxide and biphenyl is improved bythe addition of monomethyl or monoethylbiphenyl.

U.S. Pat. No. 3,907,696 issued to Jackson et al. on Sep. 23, 1975,discloses heat transfer agents containing at least three componentsconsisting of by volume 5 to 90 percent diphenyl oxide, 5 to 50 percentbiphenyl and 5 to 90 percent polyphenyl ether having 3 or 4 aromaticnuclei, alkylated biphenyl or diphenyl oxide having 1 to 4 methyl orethyl substituents, ethylbenzene oil and mixtures thereof.

U.S. Pat. No. 3,888,777 issued to Jackson et al. on Jun. 10, 1975,discloses a three-component heat transfer agent containing 5 to 90percent diphenyl oxide, 5 to 50 percent biphenyl and 5 to 90 percentbiphenylyl phenyl ether.

U.S. Pat. No. 3,243,380 issued to Conn on Mar. 29, 1966, discloses amethod of decontaminating an aromatic hydrocarbon liquidmoderator-coolant. For evaluation purposes, liquid triphenyl productswere used with determined amounts of dibenzothiophene admixed.

U.S. Pat. No. 3,113,090 issued to Ort et al. on Dec. 3, 1963, disclosesa composition for cooling neutronic reactor comprising polyphenyl andanthracene. Polyphenyl is defined in the patent to include biphenyl,terphenyls, alkylation products thereof and mixtures thereof.

U.S. Pat. No. 2,883,331 issued to Bolt et al. on Apr. 21, 1959,discloses inhibited reactor coolants comprising certain polynucleararomatic hydrocarbons, certain aryl selenium and sulfur compounds. Thecertain aryl selenium and sulfur compounds contain at least two phenylrings and at least one sulfur or selenium atom or both, the compoundsbeing substantially free of elements other than C, H, S and Se. Suitablepolynuclear aromatic hydrocarbons include biphenyl and naphthalene.

U.S. Pat. No. 2,033,702 issued to Grebe et al. on Mar. 10, 1936,discloses a heat transfer agent comprising a mixture of polynucleararomatic hydrocarbons higher than diphenyl which is formed through thecondensation between benzene and/or diphenyl in the manufacture ofdiphenyl by pyrolysis of benzene. The material is obtained as a residueafter distilling off unreacted benzene and diphenyl product from thereacted mixture. The patent describes that the exact composition of theresidual mixture is not known, but it contains a considerable proportionof triphenyl, tetraphenyls, etc.

U.S. Pat. No. 1,972,847 issued to Levine et al. on Sep. 4, 1934,discloses a stable heat transfer medium comprising diphenyl oxide,naphthalene and diphenyl.

U.S. Pat. No. 1,882,809 issued to Grebe on Oct. 18, 1932, discloses aheat transfer fluid having a hiqh boiling point and a low freezing pointcomprising diphenyloxide and diphenyl. Grebe mentions that after usingthe fluid continuously for some time, a gradual decomposition will occurwherein products of higher and lower boiling points will be formed, andthat the formation of such decomposition products still further lowersthe final freezing point of the mixture.

U.S. Pat. No. 1,874,258 issued to Dow on Aug. 30, 1932, discloses aheating fluid which consists of diphenyl oxide, diphenylene oxide (alsoknown as dibenzofuran), and, optionally, diphenyl or naphthalene.

French Patent No. 960,087 issued to the Standard-Thomson Corporation ofthe United States on Oct. 17, 1949, discloses liquids for fillingthermostatic devices which include a mixture which is essentially theeutectic mixture of diphenyl ether with two or three of the followingcompounds: diphenyl, metaterphenyl, orthoterphenyl, and benzophenone.

It is, therefore, an object of the present invention to provide afunctional fluid composition (a) which is useful as either aheat-transfer fluid, a lubricant, or a hydraulic fluid, and the like,(b) which has a low freezing point and a high maximum recommended usetemperature, (c) which contains components which are mutually solubleand capable of preparing homogeneous mixtures, (d) wherein thecomponents have relatively close boiling points for easier recovery andpurification by distillation, and (d) which are made from readilyavailable materials.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the invention, these andother objects and advantages are addressed as follows.

A functional fluid composition is disclosed which comprises ahomogeneous mixture of diphenyl ether and benzophenone and at least oneadditional component selected from the group consisting of dibenzofuranand naphthalene. In a more specific embodiment, a functional fluidcomposition is disclosed which comprises a homogeneous mixture ofdiphenyl ether employed in an 1 amount from about 5 to about 80 weightpercent, benzophenone employed in an amount from about 5 to about 50weight percent, and at least one additional component selected from thegroup consisting of dibenzofuran and naphthalene employed in an amountfrom about 5 to about and the at least one additional component beingpresent in such quantities that the functional fluid composition isthermally stable up to at least about 650° F. and has a freezing pointof less than about 54° F.

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns a functional fluid composition which entails ahomogeneous mixture of diphenyl ether and benzophenone and at least oneadditional component selected from dibenzofuran and naphthalene. Each ofthe terms "benzophenone", "dibenzofuran", and "naphthalene" are meant toinclude both the unsubstituted compounds and the compounds substitutedwith benzoyl, phenyl, and phenoxy radicals. Preferably, the diphenylether, the benzophenone, and the additional component are present in thehomogeneous mixture in such proportions that the functional fluidcomposition has a freezing point of less than about 54° F. and isthermally stable up to at least about 650° F.

The term "freezing point" is used to mean the highest temperature atwhich solid can still appear in the fluid. In the functional fluid art,this is sometimes referred to as the "crystal point", which is thehighest temperature at which solid and liquid can exist in thermodynamicequilibrium.

With respect to thermal stability, the maximum temperature at which amaterial is considered thermally stable is considered to be the highesttemperature at which the fluid experiences less than about 5 weightpercent degradation to undesirable compounds per week. Ultimately,however, the use and the end-use application will determine how muchdegradation is acceptable at any given temperature. A detaileddescription of how to measure degradation is provided in the Exampleswhich follow.

Typically, the levels of the components of the homogeneous mixture aresuch that diphenyl ether is employed in an amount from about 5 to about80 weight percent, the benzophenone is employed in an amount from about5 to about 50 weight percent, and the additional component, that is,dibenzofuran and/or naphthalene, are each individually employed fromabout 5 to about 25 weight percent. By the term "each individuallyemployed from about 5 to a`out 25 weight percent", it is meant that bothdibenzofuran and naphthalene may be employed in the same composition andmay each be used from about 5 to about 25 weight percent of thefunctional fluid composition.

More preferred functional fluid compositions are prepared when thelevels of the components are such that diphenyl ether is employed in anamount from about 40 to about 60 weight percent, the benzophenone isemployed in an amount from about 20 to about 35 weight percent, and theadditional component, the dibenzofuran and/or naphthalene, are eachindividually employed from about 5 to about 15 weight percent.

Optionally, biphenyl may be added to the compositions of this invention.Biphenyl is favorably used in an amount from greater than 0 to about 30weight percent of the functional fluid composition. Preferably, biphenylis used from about 10 to about 20 weight percent of the functional fluidcomposition.

The eutectic compositions, or those that are near the eutecticcompositions, are the most preferred compositions of this invention. Thelevels of the components in the eutectic or near eutectic compositionsdepend upon which components are used. The following describes the mostpreferred compositions, which are also reflected in the Examplesprovided hereinbelow.

One preferred composition contains (a) diphenyl ether employed in anamount from about 50 to about 60 weight percent, (b) benzophenoneemployed in an amount from about 28 to about 38 weight percent, and (c)naphthalene employed in an amount from about 7 to about 17 weightpercent.

A second preferred composition Contains (a) diphenyl ether employed inan amount from about 49 to about 59 weight percent, (b) benzophenoneemployed in an amount from about 27 to about 37 weight percent, and (c)dibenzofuran employed in an amount from about 9 to about 19 weightpercent.

A third preferred composition contains (a) diphenyl ether employed in anamount from about 42 to about 52 weight percent, (b) benzophenoneemployed in an amount from about 23 to about 33 weight percent, (c)naphthalene employed in an amount from about 5 to about 15 weightpercent, and (d) biphenyl employed in an amount from about 11 to about21 weight percent.

A fourth preferred composition contains (a) diphenyl ether employed inan amount from about 41 to about 51 weight percent, (b) benzophenoneemployed in an amount from about 22 to about 32 weight percent, (c)dibenzofuran employed in an amount from about 6 to about 16 weightpercent, and (d) biphenyl employed in an amount from about 11 to about21 weight percent.

A fifth preferred composition contains (a) diphenyl ether employed in anamount from about 44 to about 55 weight percent, (b) benzophenoneemployed in an amount from about 24 to about 34 weight percent, (c)dibenzofuran employed in an amount from about 7 to about 17 weightpercent, and (d) naphthalene employed in an amount from about 5 to about15 weight percent.

A sixth and the most preferred composition contains (a) diphenyl etheremployed in an amount from about 37 to about 47 weight percent, (b)benzophenone employed in an amount from about 20 to about 30 weightpercent, (c) dibenzofuran employed in an amount from about 5 to about 15weight percent, (d) naphthalene employed in an amount from about 4 toabout 14 weight percent, and (e) biphenyl employed in an amount fromabout 9 to about 19 weight percent.

Optionally, additional components, such as anthracene, phenanthrene, o-,m-, and p-benzoylbiphenyl, o-, m-, and p-benzoylphenyl phenyl ether, 1-and 2-benzoylnaphthalene, and fluorene may be added to the functionalfluid compositions of this invention. Benzoyl, phenyl-, andphenoxy-substituted naphthalenes, dibenzofurans and benzophenones arealso useful additives for the compositions.

The compositions of the present invention may also contain impuritiesthat normally occur in the production and isolation of the individualcomponents. Some of the impurities that may be expected include1-methylnaphthalene, 2-methylnaphthalene, fluorene, anthracene,phenanthrene, phenol, 2-methylbiphenyl, 3-methylbiphenyl,4-methylbiphenyl, 2-methylphenyl phenyl ether, 3-methylphenyl phenylether, 4-methylphenyl phenyl ether, and diphenylmethane. Generally,impurities should be present in an amount less than about 5 weightpercent based on the weight of the functional fluid composition,preferably, in an amount less than about 1 weight percent.

Advantageously, the components of the compositions of this inventionhave boiling points relatively close which makes recovery andpurification by distillation easier. The boiling point of diphenyl etheris 258.3° C.; of benzophenone, 305.9° C., of dibenzofuran, 287°-288° C.;of naphthalene, 218.0° C.; and of biphenyl, 256.1° C. Therefore, theboiling points of the components are generally within a 100° C. range.

The compositions of this invention normally have boiling points ofgreater than about 200° C. The high boiling points are beneficial inthat high vapor pressures are avoided which require high-pressureprocessing equipment.

To form the compositions of this invention, the components may be mixedin any manner and in any order desired. For examples of suitable methodsof mixing: (a) the components may first be melted before mixing, (b) onecomponent may be melted and the other components added as solids, or (c)the components may be mixed as solids. The solid mixture or a slurry ofsolid components in liquid may be heated to accelerate mixing anddissolution.

The compositions of this invention may be optimized or formulated to bethe precise eutectic mixture. One way to optimize is to 1) freeze asample of a composition which is close to what is believed to be theeutectic composition, 2) thaw the sample and draw off the portion whichmelts first, 3) analyze the composition of the drawn-off portion, 4)prepare a new sample having the composition of the drawn-off portion, 5)freeze the new sample and 6) repeat steps 2-5 until the composition ofthe sample matches the drawn-off portion. The eutectic mixture typicallymelts over a 1°-2° C. range.

Thus, there is provided in accordance with the present invention, afunctional fluid composition (a) which is useful as either aheat-transfer fluid, a lubricant, or a hydraulic fluid, and the like,(b) which has a low freezing point and a high maximum recommended usetemperature, (c) which contains components which are mutually solubleand capable of preparing homogeneous mixtures, (d) wherein thecomponents have relatively close boiling points for easier recovery andpurification by distillation, and (d) which are made from readilyavailable materials.

The following examples are illustrative only and should not be construedas limiting the invention which is properly delineated in the appendedclaims.

EXAMPLES

The compositions in the following examples are believed to be close tothe eutectic compositions for the components used as it was found thatthe compositions melted over a relatively narrow temperature range.However, the formulations may be further optimized to arrive at acomposition having the minimum freezing point for the given components.

The freezing points of the various compositions prepared in the exampleswere measured by starting with a sample of the given composition cooledto a temperature where it was completely frozen. Seed crystals of allthe components present in the composition were added to ensure completefreezing. The temperature of the frozen sample was then increased insuch a manner that it was believed to maintain the sample in thermal andsolid/liquid equilibrium. To increase the temperature, the sample wasplaced in a constant-temperature freezer or bath, and the temperaturewas raised 1° or 2° F. every few days. During the period of increasingthe temperature, the sample was agitated by periodic shaking.

EXAMPLES 1-6

The functional fluids having the compositions given in Table 1 wereprepared. The functional fluids prepared were colorless to pale yellowclear liquids at room temperature. The freezing point for eachcomposition was measured and is also provided in Table 1.

                  TABLE 1                                                         ______________________________________                                        Weight Percent in Composition                                                                              FP.sup.f                                         Example DPE.sup.a                                                                             BP.sup.b                                                                              Naph.sup.c                                                                          DBF.sup.d                                                                            BZP.sup.e                                                                           °F.                         ______________________________________                                        1       55.19   0       11.95 0      32.86 38                                 2       54.03   0       0     13.73  32.24 37                                 3       46.71   15.76    9.91 0      27.62 27                                 4       45.99   15.50   0     11.34  27.17 25                                 5       48.68   0       10.39 12.09  28.84 28                                 6       42.10   14.08    8.83 10.20  24.79 17                                 ______________________________________                                         .sup.a diphenyl ether                                                         .sup.b biphenyl                                                               .sup.c naphthalene                                                            .sup.d dibenzofuran                                                           .sup.e benzophenone                                                           .sup.f freezing point                                                    

EXAMPLE 7

The components of the compositions of this invention can degradesomewhat to other compounds, especially when maintained at very hightemperatures. In general, a mixture of components is said to degrade nofaster than the least stable component in the mixture. Therefore, todetermine the thermal stability of the compositions of this invention,degradation rates of the individual components of the compositions weremeasured at 750° F. To measure the degradation rate of each component,several glass ampoules measuring about 8 mm o.d. by about 25 cm inlength were each filled with about three grams of the component underinvestigation. The ampoules were attached to a vacuum line, and sampleswere cooled to -78° C. by immersion into an insulated vessel containingdry ice and methylene chloride. The ampoules were then evacuated to lessthan 70 millitorr and sealed with a torch. The sealed ampoules were eachplaced in a 1/2" o.d. stainless steel tube. About three grams of theheater-transfer fluid, "DOWTHERM A", (available from the Dow ChemicalCompany, Midland, Mich., owner of the trademark "DOWTHERM A") wereplaced in each stainless steel tube and the remaining end of thestainless steel tubes were capped closed. The filled stainless steeltubes were then placed in a circulating-air oven which was heated to the750° F. Ampoules were periodically removed and their contents analyzedby capillary gas chromatography. The analysis was corrected to take intoaccount the amount of material actually recovered from the ampoule. Thecorrected recovered starting material values were plotted versus timeand a linear least squares regression analysis was done to obtain thedegradation rates.

Table 2 provides the degradation rates per week of the individualcomponents of the present invention measured at 750° F. If thedegradation rate of a mixture is desired, the same procedure describedabove should be followed, except that the starting composition of thefluid needs to be determined before heating.

                  TABLE 2                                                         ______________________________________                                                       Degradation Rate                                                              at 750° F.                                              Compound       (percent/week)                                                 ______________________________________                                        Diphenyl ether 1.15                                                           Biphenyl       1.05                                                           Naphthalene    0.88                                                           Dibenzofuran   2.25                                                           Benzophenone   2.7*                                                           ______________________________________                                         *The degradation rate of benzophenone was determined at 700° F.   

While my invention has been describe in terms of specific embodiments,it must be appreciated that other embodiments could readily be adaptedby one skilled in the art. Accordingly, the scope of my invention is tobe limited only by the following claims.

What is claimed is:
 1. A functional fluid composition, comprising a homogeneous mixture of from about 5 to about 80 weight percent diphenyl ether and from about 5 to about 50 weight percent benzophenone and from about 5 to about 25 weight percent of at least one additional component selected from the group consisting of dibenzofuran and naphthalene.
 2. The functional fluid composition of claim 1, wherein the diphenyl ether, the benzophenone, and the at least one additional component are in proportions such that the functional fluid composition is thermally stable up to at least about 650° F.
 3. The functional fluid composition of claim 1, wherein the diphenyl ether, the benzophenone, and the at least one additional component are in proportions such that the functional fluid composition has a freezing point of less than about 54° F.
 4. The functional fluid composition of claim 1, further comprising biphenyl employed in an amount from greater than 0 to about 30 weight percent.
 5. The functional fluid composition of claim 1, wherein the diphenyl ether is employed in an amount from about 40 to about 60 weight percent, the benzophenone is employed in an amount from about 20 to about 35 weight percent, and the at least one additional component is employed in an amount from about 5 to about 15 weight percent.
 6. The functional fluid composition of claim 5, wherein the at least one additional component includes a combination of both dibenzofuran and naphthalene individually employed in amounts from about 5 to about 15 weight percent.
 7. The functional fluid composition of claim 6, further comprising biphenyl employed in an amount from about 10 to about 20 weight percent.
 8. A functional fluid composition, comprising a homogeneous mixture of diphenyl ether employed in an amount from about 5 to about 80 weight percent, benzophenone employed in an amount from about 5 to about 50 weight percent, and the at least one additional component selected from the group consisting of dibenzofuran and naphthalene employed in an amount from about 5 to about 25 weight percent, the diphenyl ether, the benzophenone, and the at least one additional component being present in such quantities that the functional fluid composition is thermally stable up to at least about 650° F. and has a freezing point of less than about 54° F.
 9. The functional fluid composition of claim 8, further comprising biphenyl employed in an amount from greater than 0 to about 30 weight percent.
 10. The functional fluid composition of claim 8, wherein the at least one additional component includes a combination of dibenzofuran and naphthalene individually employed in amounts from about 5 to about 15 weight percent.
 11. The functional fluid composition of claim 10, further comprising biphenyl employed in an amount from about 10 to about 20 weight percent.
 12. The functional fluid composition of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 50 to about 60 weight percent; (b) benzophenone employed in an amount from about 28 to about 38 weight percent; and (c) naphthalene employed in an amount from about 7 to about 17 weight percent.
 13. The functional fluid composition of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 49 to about 59 weight percent; (b) benzophenone employed in an amount from about 27 to about 37 weight percent; and (c) dibenzofuran employed in an amount from about 9 to about 19 weight percent.
 14. The functional fluid composition, of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 42 to about 52 weight percent; (b) benzophenone employed in an amount from about 23 to about 33 weight percent; (c) naphthalene employed in an amount from about 5 to about 15 weight percent; and (d) biphenyl employed in an amount from about 11 to about 21 weight percent.
 15. The functional fluid composition, of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 41 to about 51 weight percent; (b) benzophenone employed in an amount from about 22 to about 32 weight percent; (c) dibenzofuran employed in an amount from about 6 to about 16 weight percent; and (d) biphenyl employed in an amount from about 11 to about 21 weight percent.
 16. The functional fluid composition, of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 44 to about 55 weight percent; (b) benzophenone employed in an amount from about 24 to about 34 weight percent; (c) dibenzofuran employed in an amount from about 7 to about 17 weight percent; and (d) naphthalene employed in an amount from about 5 to about 15 weight percent.
 17. The functional fluid composition, of claim 1, wherein the homogeneous mixture contains:(a) diphenyl ether employed in an amount from about 37 to about 47 weight percent; (b) benzophenone employed in an amount from about 20 to about 30 weight percent; (c) dibenzofuran employed in an amount from about 5 to about 15 weight percent; (d) naphthalene employed in an amount from about 4 to about 14 weight percent; and (e) biphenyl employed in an amount from about 9 to about 19 weight percent. 